The present invention relates to a discharging laser apparatus, and more particular to a discharge electrodes connecting structure in a laser apparatus and a laser apparatus provided with the discharge electrodes.
Conventionally, there has been known a discharge exciting laser apparatus which generates a discharge between discharge electrodes so as to excite a laser medium, thereby oscillating a laser beam, and the discharge exciting laser apparatus is, for example described in Unexamined Japanese Patent Publication No. 1-268078. FIG. 6 shows a structure of an excimer laser apparatus disclosed in the publication, and FIG. 7 shows a discharge electrode structure of the excimer laser apparatus disclosed in the publication.
In FIGS. 6 and 7, an excimer laser apparatus 101 is provided with a laser chamber 102 for sealing a laser medium such as a laser gas or the like. A pair of discharge electrodes 105A and 105B constituted by an anode 105A and a cathode 105B are arranged in an inner portion of the laser chamber 102 in an opposing manner. The anode 105A is fixed to a conductive anode base 106 and the cathode 105B is fixed to an insulative cathode base 108, respectively. A discharge is generated between the anode 105A and the cathode 105B so as to excite a laser gas shown by an arrow G flowing between the discharge electrodes 105A and 105B, thereby oscillating a laser beam.
Auxiliary ionization electrodes 118 and 118 are respectively arranged in both sides of the discharge electrodes 105A and 105B in an opposing manner, to which a high voltage current is supplied from a high voltage power source via an auxiliary ionization circuit and a current introduction terminal (not shown), thereby performing an auxiliary ionization.
The anode base 106 and the cathode base 108 are supported to keep a predetermined interval by a supporting post 110. Further, the anode base 106 and the laser chamber 102 are electrically connected by a plurality of return plates 109 arranged in a longitudinal direction of the discharge electrode to keep a predetermined interval. In this case, a connecting portion between a return plate 109 and the laser chamber is not clearly illustrated in the publication mentioned above. The return plate 109 is constituted by a conductive sheet member and is arranged in parallel to the gas flow G so as not to prevent the gas flow of the laser gas between the discharge electrodes 105A and 105B and so that a thin portion 109A is directed to an upstream side and a downstream side of the gas flow G with respect to the gas flow.
Further, a once through fan 114 for feeding the laser gas to a portion between the discharge electrodes 105A and 105B, and a heat exchanger 103 for cooling the laser gas heated between the discharge electrodes 105A and 105B due to the discharge are respectively arranged at predetermined positions within the laser chamber 102.
However, the conventional art disclosed in Unexamined Japanese Patent Publication No. 1-268078 has the following problems.
That is, in the conventional art, there is a description that the return plate 109 is formed in a thin sheet shape, a resistance of the laser gas is reduced and a rectifying effect for rectifying the gas flow G of the laser gas is expected as a thickness of the return plate 109 becomes thinner. However, it is known that when making the return plate 109 too thin, the return plate 109 vibrates due to the gas flow G so as to prevent the gas flow G and reduce a flow speed. Accordingly, the discharge becomes unstable and a power of the laser beam changes. Further, when making the thickness of the return plate 109 too thin, the resistance of the current flowing through the return plate 109 is increased, so that the discharge is not properly performed.
The present invention is made by solving the problems in the technique mentioned above, and an object of the present invention is to provide a discharge electrodes connecting structure for a laser apparatus in which a thickness of the return plate is set to be within an optimum range, and a laser apparatus employing the same.
In order to achieve the object mentioned above, in accordance with the present invention, there is provided a discharge electrodes connecting structure for a laser apparatus comprising:
a pair of anode and cathode provided within a laser chamber for sealing a laser gas in an opposing manner, generating a discharge so as to excite a laser gas flowing therebetween and oscillating a laser beam;
a conductive anode base holding the anode;
an insulative cathode base holding the cathode; and
a return plate electrically connecting the anode base to the laser chamber so as to supply a current to the anode and having a thickness of equal to or more than 100 xcexcm and equal to or less than 500 xcexcm.
Further, in accordance with the present invention, there is provided a laser apparatus comprising:
a laser chamber sealing a laser gas;
discharge electrodes constituted by a pair of anode and cathode provided within the laser chamber in an opposing manner, generating a discharge so as to excite a laser gas flowing therebetween and oscillating a laser beam;
a conductive anode base holding the anode;
an insulative cathode base holding the cathode; and
a return plate electrically connecting the anode base to the laser chamber so as to supply a current to the anode
wherein a thickness of the return plate is set to be equal to or more than 100 xcexcm and equal to or less than 500 xcexcm, and the return plate is arranged substantially in parallel to a gas flow of the laser gas flowing between the discharge electrodes.
In accordance with the structure mentioned above, since the thickness of the return plate is made thin to a level equal to or less than 500 xcexcm and the return plate is arranged in parallel to the gas flow, the return plate hardly disturb the gas flow of the laser gas flowing between the anode and the cathode. Further, since the thickness of the return plate is set to be equal to or more than 100 xcexcm, the return plate does not vibrate due to the gas flow. Further, since the thickness of the return plate is made thicker than an entering depth of a high frequency current flowing on a surface of the return plate at a time of discharging, a resistance of the current is not increased and the discharge can be properly performed. Accordingly, the discharge becomes stable and a power of the laser beam becomes stable.